مهندسی مکانیک شریف (Jun 2024)
Experimental determination of correction factors from Charpy impact testing of API X65 steel with varying specimen thickness
Abstract
The purpose of this research, in addition to determining the characteristic forces, including the yield force and maximum force, was to calculate the correction factors to predict the onset of failure in the energy transmission pipelines with high toughness under dynamic (impact) loading. To achieve this goal, an instrumented Charpy impact machine, which plots the force-displacement diagram during the impact test, was used. Then, by dividing the area under the force-displacement diagram into two parts, both the initiation energy and crack growth energy in API X65 steel were calculated. The results showed that the total energy provided by the machine dial was in agreement with the total energy calculated from the area under the force-displacement curve. Characteristic forces were also determined from the force-displacement curve as described in the BS 14556 standard. After that, power law expressions with high accuracy were extracted to describe the behavior of the tested steel against variations of the Charpy sample thickness for crack initiation energy, crack propagation energy, and characteristic forces. Additionally, the average correction factor, which is used in prediction models of energy transmission steel pipelines, was found to be 1.26, which is in good agreement with the available results for the current steel in the literature. It was shown that by increasing the thickness, due to the transition from plain stress to plain strain condition, the correction factor changed from 1.26 to 1.3 in 8 to 10 mm thicknesses, while it did not change so much from 4 to 8 mm thicknesses. By examining the characteristic forces and plotting the ratio of the yield force to the maximum force versus thickness variation, it was also found that increasing the thickness leads to decreasing the work hardening of the steel.
Keywords
